1. Field of the Invention
This invention relates to apparatus for marking a workpiece and, more particularly, to a method and apparatus for supporting a marking device for movement on a frame through a plurality of degrees of movement to position the marking device to selectively impress identification marks on the surfaces of the workpieces being conveyed in a production line.
2. Description of the Prior Art
Machines for impressing identification marks on the surface of billets, slabs, plates, bars, ingots, and the like are well known in the art. In one known arrangement, the workpiece to be marked is conveyed by a roll table beneath the marking machine in a production line as disclosed in U.S. Pat. Nos. 3,541,954; 3,636,871 and 4,036,127. These devices include a marking device that carries marking elements which are moved into impact relation with the surface of the workpiece to impress an array of alphanumeric characters on the workpiece as the workpiece is conveyed in the production line. It is essential that the workpiece be marked without interrupting the production line.
One well known type of marking device is a single wheel marker that includes a marking wheel that carries a plurality of marking characters or elements on the peripheral surface thereof. An example of a single wheel marker is illustrated in U.S. Pat No. 4,214,520. U.S. Pat. Nos. 3,306,186; 3,541,954 and 3,636,871 discloses similar devices in which a marking head includes a plurality of marking wheels for marking billets, slabs, bars, rolled stock and the like.
With both single and multiple marking wheel markers, the respective marking wheel is rotated until the desired character on the wheel periphery is in marking position. The wheel is held in position by a suitable locking device and, thereafter, an actuator is remotely actuated to move the marking wheel to strike the billet and impress the selected character thereon. The marking wheel is then retracted and the wheel is incrementally rotated and moved laterally to the next position for marking the billet. The actuator is sequentialy operated to move the marking head so that the character is stamped on the surface of the billet. This operation is repeated through the required sequence of steps to impress a series of marks on the billet.
Once the billet has been marked, the next billet must be moved into position for marking. This requires the marking head to be withdrawn to facilitate the movement of the next billet into position as rapidly as possible so that a number of billets can be marked in rapid succession. To accomplish this the marking wheel must be efficiently moved into and out of the marking position. Further, after each billet is marked, the sequence of characters must be changed. This requires moving the marking wheel to stamp the billet and rotating the marking wheel to place the next desired character in marking position. Once the desired series of characters have been impressed on the billet by incremental lateral movement of the marking wheel, it is necessary to return the marking wheel to the initial marking position for marking the next billet.
Thus in order to successfully mark a plurality of workpieces moving successively in a production line, the marking device must be supported for rapid movement into and out of the marking position. The marking characters must be rapidly changed on the marking head to permit marking the workpieces in rapid succession without interrupting the movement of the workpieces in the production line. Consequently, delays in the movement of the marking device into and out of the marking position and changing of the marking characters on the marking head will interrupt the production line.
More recently, in an effort to increase the speed of the marking operation and to reduce the time required to change the combination of alphanumeric characters for a message to be inscribed, non-contact markers, such as ink jet or spray printers, have been utilized. However, their use has been predominantly confined to imprinting on a recording medium, such as paper. Known ink jet or spray markers are disclosed in U.S. Pat. Nos. 3,787,884; 4,272,733; 4,356,499; 4,376,284; 4,412,232; and 4,415,909.
In particular, U.S. Pat. No. 4,412,232 discloses a wheel which is rotatably mounted on a housing of a printhead to support the housing for manual movement over the surface of the medium onto which characters are to be printed. The printhead contains a plurality of nozzles which are actuated by movement of the wheel on the surface of the recording medium. The nozzles are arranged in a straight line extending transversely to the direction of the printhead movement. Data processing equipment provides signals to control driver circuits to uniformly print the desired characters in the dot matrix pattern.
U.S. Pat. No. 4,415,909 discloses an ink jet printer having an arrangement of nozzles in a symmetrical pattern. A drive element is associated with each nozzle, and a piezoelectric crystal initiates the formation of ink droplets by pulsing the ink supply inside a tube associated with each nozzle and causing the ink to be ejected from the nozzle in droplet form. The nozzle array is formed in a pattern to generate equally separated rows of dots on the record media or paper. The printhead is moved along a line of printing with the line of symmetry being at an angle relative to the direction of motion to produce a vertical column of dots perpendicular to the direction of movement. The times for energizing the individual print elements is controlled to minimize the gap between the nozzles to thus enable dot matrix type printing.
While the prior art devices disclose marking machines that utilize single and multiple marking wheel markers for impressing identification marks on billets, slabs, bars and the like, the speed at which the wheels are moved into and out of position and the movement of the wheels to change the series of characters to be marked limit the rate at which the workpieces to be marked are advanced in the production line. Therefore, there is need for a marking machine for use in high speed marking of workpieces in a production line where the workpieces are successively marked by dot matrix characters in which the make up of the characters to be stamped on the workpiece is quickly adjusted from one workpiece to another without interrupting movement of the workpieces in the production line.